1. Field of the Invention
The invention relates to latent combination compounds comprising epoxide resin curing agents and flame-protection agents. Furthermore, it relates to a process for reacting these latent combination compounds with water and/or mono- or polyhydric hydroxy compounds, and the latent ammonium salts formed during this reaction. Selected latent ammonium salts can be obtained according to an alternatively presented process. The latent combination compounds and latent ammonium salts can be used in the preparation of single-component resin systems, and moulded bodies and coatings with flame-retarding properties obtainable from them, in heat-curable single-component epoxide resin adhesives and in resin-injection processes. The invention furthermore covers prepregs and composite materials as well as printed wiring boards.
2. The Prior Art
There is a demand for epoxide resin systems which can be used in resin-injection processes, and which cure completely at as low as possible a defined temperature, have excellent material properties and are toxicologically harmless in case of fire. The known epoxide resin systems are not satisfactory in this respect, in particular problems arise during storage, as the cured systems do not have the desired mechanical properties and are not toxicologically harmless in case of fire.
Currently, only a few epoxide resin systems are known which can be used in resin-injection processes. In the case of Ciba-Geigy""s RTM6 system, curing takes place at too high a temperature (180xc2x0 C.) over too long a period (2 hours). A single-component epoxide resin system based on a diglycidyl ether of fluorene bisphenol from 3M is known. Although this system has good fracture mechanics values, it also cures only at 180xc2x0 C. Bayer AG supplies under the trade name Blendur(copyright) an epoxiisocyanurate resin, based on diphenylmethane diisocyanate, which offers the possibility of curing at different temperatures. Through a secondary curing, again at too high a temperature (200xc2x0 C.), the corresponding properties can then be achieved.
Low-temperature-curing epoxide resin systems (curing at approx. xe2x88x92100xc2x0 C.) with a sufficiently high glass transition temperature (Tg approx. 200xc2x0 C.) can be obtained if a highly exothermic polymerization is achieved. This is facilitated above all by anionic homopolymerization of the epoxide resins. Particularly good results are obtained when the polymerization starters, often called accelerators in epoxide resin chemistry, are released rapidly or suddenly. This principle is called latent acceleration and is carried out in single-component resins. In epoxide resin chemistry, these accelerators are deactivated by mechanical encapsulation or through the formation of chelate complexes. By increasing the temperature, the actual accelerator substances are released again. It is decisive in particular for use in resin-injection processes that this release occurs extremely abruptly. This is an essential precondition if the resin systems are to have good flow properties during processing at increased temperature (60 to 800xc2x0 C.) but cure rapidly after a slight further temperature increase (to say 100xc2x0 C.).
It is known to the person skilled in the art that the terms curing agent and accelerator are not clearly distinguishable from each other in epoxide resin chemistry; above all, the substances which are added to epoxide resin systems cannot be allocated either a curing or an acceleration effect. Both terms, xe2x80x9ccuring agentxe2x80x9d and xe2x80x9cacceleratorxe2x80x9d, are therefore used when describing this invention in order to express the capacity of the presented substances to cure any epoxide resin system or accelerate curing.
The known single-component resins which can be latently accelerated contain Lewis adducts of tertiary amines and do not fulfil the requirements. They must be stored at low temperatures and accelerate the polymerization unevenly so that a secondary tempering is required after the actual polymerization.
The documents U.S. Pat. No. 3,632,427, U.S. Pat. No. 3,642,698, U.S. Pat. No. 3,635,894 and U.S. Pat. No. 3,678,007 disclosed salts of imidazoles with mineral acids. EP 0 589 166 B1 and EP 0 589 167 B1 disclose the preparation of transition metal/heterocycle complexes which are proposed as latent polymerization catalysts for epoxide resins. The compounds mentioned are however solids which must be dissolved in solvents and their use in single-component resins, their use in resin-injection processes and in composite materials is ruled out as separation leads to unavoidable problems which impair the mechanical properties of the epoxide resin material and product.
For high-performance applications, additional modification agents (modifiers) are required in order to satisfy special requirements in terms of physical and material properties. This involves above all an improvement in elasticity (NBR modifiers) and behaviour in fire (FST modifiers).
Modern epoxide resins as well as products prepared from them must above all have flame protection. The state of the art in the case of flame protection of epoxide resins is the use of non-reactive flame protection agents such as aluminium hydroxide, magnesium hydroxide, ammonium polyphosphate or red phosphorus in the case of casting compounds and coatings. They are economical and toxicologically harmless. To achieve sufficient flame protection however, relatively large amounts must be added. As these flame protection agents do behave like non-reactive fillers and the mechanical properties are clearly impaired, they are not used in composite materials. Furthermore, they are not suitable for resin-injection processes as the fabric to be impregnated acts as a filter on the flame protection agent. The state of the art in the case of composites is the use of epoxide resins which have been reacted with tetrabromobisphenol A. Antimony trioxide is also often used as a synergist. In case of fire, however, brominated dioxins can form. In addition, the scene of the fire is contaminated with carcinogenic antimony fly ash and highly corrosive acids.
Flame-protection agents which can be reactively incorporated into epoxide resin are known from DE 44 47 277 A1, DE 43 08 184 A1 and EP 0 806 429 A2. Epoxide resin systems to which these flame-protection agents have been added are however unsatisfactory as regards their processing properties, above all pre-reacted epoxide resins are moisture-sensitive and not storage-stable.
The object of the present invention is therefore to provide single-component epoxide resin systems for manufacturing products given flame-retarding properties, with which the simple selection of a particular desired curing temperature must be possible. The epoxide resin systems are themselves to display excellent storage-stability, above all long-term storage-stability and be able to be used in resin-injection processes. The novel epoxide resin materials obtained by curing are to have excellent mechanical properties, e.g. fracture resistance and low brittleness, and simultaneously have excellent flame-protection properties without being toxicologically harmful in case of fire.
It was surprisingly found that this object is achieved by novel chemical compounds.
The invention relates inter alia to a group of phosphinic acid amides for which the term xe2x80x9clatent combination compoundsxe2x80x9d is also used in the following, on the other hand a group of ammonium phosphinates which are also called xe2x80x9clatent ammonium saltsxe2x80x9d. Common to the presented chemical compounds according to the invention is that they are capable, upon a temperature increase, of curing the epoxide resin system to which they have been added, i.e. they are latent curing agents/accelerators; simultaneously, they facilitate the flame-proofing of the epoxide resin and of the products prepared from it.